I don't think Republic would have ever considered an in-line engine on their designs. In de Servesky's book "Victory Through Airpower" he refers to the "Allison inline" as the "Air Corps pet engine," perhaps he had some bitter feeling towards the USAAC as he made this statement after he was removed as Serversky's CEO. I think its safe to say that Kartiveli was intent on designing fighters around radials.

My take is that with non-turbo V-1710 the gain is practically nil - just another plane that's good for combats under 15 kft, but a bad choice for combats above that alt.

Now, replacing R-1830 with V-1710, in P-43, offers some better performance, at least on paper. P-38F was served with 1325 HP at 20 kft, 1240 HP at 25 kft, in second half of 1942, so we can use that power for 'our' P-43. Such power was comparable with Merlin 60s, but those can go to WEP (or 5min regime?) for more power, albeit at lower height. The P-43 itself was Spitfire-sized, but it was heavier than Mk.IX, let alone the Mk.V. The armament need to go to 6x .50 cals, with at least 350 rpg. Protection also need to be more substantial. That would mean some 500-1000 lbs more for take off - 8000-8500 lbs 'loaded' weight? Heavy indeed, but still some 10% than P-51D.
My take is that top speed would've been something between Spit V and IX (390 mph at 25 kft? - turbo cancels the exhaust thrust mostly), with climb comparable with P-51D, available from late 1942 on. That's with P-38 engine power for era; from late 1943, it's 1425 HP MIL (400 mph +?), and 1600 HP WER (410-420 mph?).

Only US plane that was really fast at altitude, prior second half of 1943, was P-38. Splendid plane, but not that available, with many bugs to sort out. A more affordable plane, to bulk out the numbers, but of similar performance, available a full year before P-47, or 15 months prior P-51B, would've been very good for Allied cause. Of course, providing it was offering a substantial internal fuel capacity (218 gals - non-self sealing in real P-43?); 2 x 108 gals drop tanks at such a plane would've take one further away than when attached at real P-47.

Turbo R-2800 was to offer 2000 HP all the way to 25000ft, turbo V-1710 was cleared for more than 1150 HP only from mid/late 1942 - no wonder AAC changed their mind and wanted the 2800 in a new fighter from mid 1940. Hence the (X)P-47B was created.

The Allison V-1710 was a decent engine when fitted with a two stage, infinetly vairable supercharger as used in the P-40Q.

Why would it take Allison 2 years after the start of the war to offer variable speed supercharger (either 2 speeds or hydraulic) let alone two stages when every American radial offered a choice of two speeds, often two stages as a further option or turbo as another option.

Granted it wasn't going to completely make up for the P-40/Me 109 weight difference but it would have given more power at all altitudes through a better matching of blower power to requirements.

Do you have any proof of this bit of "folk lore". Allison did have to "forget" $900,000 of "government" debt for permission to export the V-1170. With dozens of different Allison models, some with many changes between models I think congress was just a little busy during the war to micro manage an engine program.

The single speed Allisons were essentially altitude engines anyway. Without a new supercharger (inlet, impeller, housing, etc) the best you were going to get was the 9.60 gears and the 15,500ft critical altitude. a "second" gear would have been a low altitude gear like 6.5 or 7.0 to 1 which would have given more power for take off and low altitudes, perhaps another 75-100hp? Since the Allison seemed to stand up to over boosting at the lower altitudes rather well this really wasn't desperately needed.
3000rpm X 9.60 gears = 28,800 impeller rpm. 9.5in dia impeller = 29.83in/2.485ft circumference. 28,800rpm X 2.485 ft / 60 (feet to seconds) = 1192fps impeller tip speed. Speed of sound at sea level at 68 degrees is about 1125-1130fps. In the higher pressure, higher temperature interior of the supercharger it is a bit higher but you aren't going to use much more tip speed in the Allison supercharger and get any real benefit.
The 2 speed (not 2 stage) Merlins used a 9:49 high gear and a 10.25in impeller. Tip speed was 1272fpm. Power used by the supercharger goes up with the square of the tip speed. 30-40% of the power used is turned into heat in the intake charge. you would need a set of 10.24 gears of the Allison to equal the tip speed of the Merlin but since the basic supercharger isn't as good as the Hooker modified supercharger on the Merlin XX you still aren't going to get the same performance.

The government didn't officially release the Allison rights until the late 1940's after the war was over for several years. By then, the V-1710 was out of production. In the 1980's the rights to the V-1710 were acquired by Rolls Royce with the intent to kill it off. But the Allison is still beating the Merlin in tractor pulls all over Europe. It got so bad that the Europen tractor pull association enacted a rule to limit the tractor enines to 1650 cubic inches, coincidentally the displacement of the Merlin.

All we did to address that was to install piston liners with 0.1 inch less bore and the displacement was magically down to 1650 and the Allisons still won. When we did that, they relented and threw out the rule, and Allisons are STILL winning tractor pulls in Europe. We have a friensd over tehre running a tractor that can use 2 or 3 Allisons , na dtheya re easily convetered between round to run in different classes.

A question about the XP-40Q-3, If I may.
I've read at the Vee's for victory that it's V-1710-121 was able to deliver 1700 bhp up to 26,000 ft. That was WER, with water/methanol injection. Was that engine featured an intercooler/aftercooler?

A question about the XP-40Q-3, If I may.
I've read at the Vee's for victory that it's V-1710-121 was able to deliver 1700 bhp up to 26,000 ft. That was WER, with water/methanol injection. Was that engine featured an intercooler/aftercooler?

Click to expand...

I think probably not.

Some 2 stage Allisons did use an intercooler, but those were the earlier ones. And I don't think they used ADI either.

The government didn't officially release the Allison rights until the late 1940's after the war was over for several years. By then, the V-1710 was out of production. In the 1980's the rights to the V-1710 were acquired by Rolls Royce with the intent to kill it off. But the Allison is still beating the Merlin in tractor pulls all over Europe. It got so bad that the Europen tractor pull association enacted a rule to limit the tractor enines to 1650 cubic inches, coincidentally the displacement of the Merlin.

All we did to address that was to install piston liners with 0.1 inch less bore and the displacement was magically down to 1650 and the Allisons still won. When we did that, they relented and threw out the rule, and Allisons are STILL winning tractor pulls in Europe. We have a friensd over tehre running a tractor that can use 2 or 3 Allisons , na dtheya re easily convetered between round to run in different classes.

A question about the XP-40Q-3, If I may.
I've read at the Vee's for victory that it's V-1710-121 was able to deliver 1700 bhp up to 26,000 ft. That was WER, with water/methanol injection. Was that engine featured an intercooler/aftercooler?

Thanks, that confirms what I was thinking.
That begs another question: what was magic behind an V-1710 developing such a power so high up (1700 HP @ 26000)? It was managing 3200 rpm, but those additional 200 rpm (IIRC) vs. 'ordinary' V-1710s seem unlikely to add 2/3 more power?

Like the XP-39 doing 390mph.
Like the P-40 being designed for ground attack.
Like the me 109K carring a MK 103 cannon and two Mg 151 15mm guns in the cowl.

You stated that " Any changes were to be approved by Congress"

On the E9 series of of engines, the first two stage engine to reach flight status the revisions to Allison specification No.137 ran from "A" to "G". Are you trying to say that each one of these changes had to approved by congress? Changes to piston rings or piston webbing had to be approved by congress? changes in vibration dampers or even a substitute carburetor or magneto had to be approved by congress?
A change in supercharger gear ratio had to be approved by congress? there were 9 different gear sets, of which 6 were used to any extent.

Owning the basic rights or controlling the export "rights" of an engine is somewhat different than having to approve every engineering change.

How successful the Allison was/is in tractor pulling competitions in the 1970s-2000s has nothing to do with wither congress had to approve engineering changes or different models of the Allison in WW II.

On the E9 series of of engines, the first two stage engine to reach flight status the revisions to Allison specification No.137 ran from "A" to "G". Are you trying to say that each one of these changes had to approved by congress? Changes to piston rings or piston webbing had to be approved by congress? changes in vibration dampers or even a substitute carburetor or magneto had to be approved by congress?
A change in supercharger gear ratio had to be approved by congress? there were 9 different gear sets, of which 6 were used to any extent.

Owning the basic rights or controlling the export "rights" of an engine is somewhat different than having to approve every engineering change.

How successful the Allison was/is in tractor pulling competitions in the 1970s-2000s has nothing to do with wither congress had to approve engineering changes or different models of the Allison in WW II.

Click to expand...

There was and still is a design change approval process for designs where the US government holds manufacturing or export rights with regards to military equipment. Things like radios, engines, turbochargers and some other accessories were supplied by the government to airframe manufacturers and was referred to as "Government Furnished Equipment" or GFE. Just because GFE was controlled by the government, there were "engineering change orders" and contract modifications to make changes to designs that were controlled by the government. One had to justify a reason for such changes and it ran through a review process that involved engineering, quialty assurance and manufacturing representatives from both the contract and government. I actually served on one of these boards when I worked for Lockheed and worked with folks who did this function during WW2.

Exactly, While an Army (or Navy) purchasing/engineering "board" may exert government control and authorize/suggest changes to equipment either already contracted for (modify contract) or to be contracted for in the future that is hardly the same as congress having to approve changes.